1. Field of the Invention
This invention relates to an elastic crawler employed for a crawler-type traveling apparatus used as a traveling unit for construction/civil engineering working machines and agricultural working machines, and to a method of producing the same.
2. Description of the Related Art
The crawler-type traveling apparatus is chiefly constituted by, for example, a drive wheel disposed on either the front side or the rear side in the direction of travel, an idler disposed on the other side, a plurality of rollers disposed between the drive wheel and the idler, and an elastic endless crawler wrapped around the drive wheel, idler and the plurality of rollers. By driving the drive wheel forward or reverse, the elastic crawler is circularly turned in the circumferential direction.
The elastic crawler employed for the crawler-type traveling apparatus includes, as shown in FIG. 6, a crawler body 6 in the form of an endless belt of a rubbery elastic material. Engaging protuberances 7 for preventing disengagement of wheels are provided on an inner circumferential side of the crawler body 6, and lugs 8 are integrally formed on an outer circumferential side of the crawler body 6.
Core metals 25 are buried in the crawler body 6 at suitable intervals in the circumferential direction A. Further, a tension member 9 is buried in the crawler body 6 for enabling the elastic crawler 5 to withstand the tension applied to the elastic crawler 5 in the circumferential direction A.
The tension member 9 may be the one in which tension cords 10 having opposite ends wound one turn along the circumferential direction A are arranged in parallel in the widthwise direction of the crawler at suitable intervals.
In the tension member 9 of this type, the tension cords 10 are longer than the whole length of the crawler body 6 in the circumferential direction A, and the ends 10a and 10b of each of the tension cords 10 are overlapped in the thicknesswise direction B of the crawler to join so that the tension cords 10 are formed into endless cords.
The elastic crawler 5 in which the opposite ends of the tension cords 10 are overlapped and joined together to form an endless shape can be produced by a method described below.
As shown in FIG. 7, first, a crawler body 11 in the form of a belt having opposite ends is formed by being primarily cured and molded in a flat plate-like mold 27.
Here, the crawler body 11 is formed with a flat surface 22 on the outer circumferential side on one end in the lengthwise direction thereof (corresponds to the circumferential direction A of the crawler), a flat surface 23 on the inner circumferential side on the other end thereof, and engaging protuberances 7 and lugs 8 formed on other portions.
Then, the flat surfaces 22 and 23 on the opposite ends of the crawler body 11 are overlapped one upon the other, and the overlapped portion is cured in a flat plate-like mold 28 having a linear cavity to thereby mold the endless elastic crawler 5 (refer to, for example, Japanese Unexamined Patent Publication No. HEI 7-223564).
According to the conventional method of production, therefore, the ends 10a and 10b of the tension cords 10 have the same length in the overlapped joint portion 12 of the tension cords 10.
In the above-mentioned conventional elastic crawler 5, a portion of the elastic crawler 5 corresponding to the overlapped joint portion 12 is molded by the flat plate-like mold 28, that is, overlapped portion of the molded crawler body 11 is cured and molded in a state where the overlapped joint portion 12 of the tension member 9 assumes the form of a straight line. As a result, when the portion of the elastic crawler 5 corresponding to the overlapped joint portion 12 is wrapped around the drive wheel, idler or rollers and deflected in a curved shape, a tensile stress acts on the ends 10b of the tension cords 10 in the overlapped joint portion 12 on the outer circumferential side of the crawler, and a compressive stress acts on the ends 10a of the tension cords 10 of the overlapped joint portion 12 on the inner circumferential side of the crawler.
The portion of the elastic crawler 5 corresponding to the overlapped joint portion 12 returns to the initial form of straight line when it moves away from the area where it is wrapped around the drive wheel or the like wheels.
This cycle of the curved state and linear state is repeated as the elastic crawler 5 is driven to be circularly turned in the circumferential direction A. When the elastic crawler 5 is used under severe conditions for extended periods of time, therefore, the adhering force between the tension cords 10 and the elastic material constituting the crawler body 6 is deteriorated in a short period of time between the ends 10a and 10b of the tension cords 10, often resulting in a peeling of the elastic material off the tension cords 10.
Further, the tension cords 10 may be broken at a boundary between the overlapped joint portion 12 and a portion where the tension member 9 is not overlapped.
In view of the above-mentioned problem, it is an object of the present invention to provide an elastic crawler having an extended life, which is not readily broken at a portion where the tension cords are overlapped due to fatigue by relieving the tensile stress acting on the outer circumferential side of the crawler and compressive stress acting on the inner circumferential side of the crawler in the overlapped portion when the elastic crawler is curved.
Technical means employed by the present invention for solving the above technical problem is an elastic crawler including a crawler body made of a rubbery elastic material in the form of an endless belt, a tension cord being buried in the crawler body along the circumferential direction thereof, the tension cord having opposite ends which are joined together by overlapping one upon the other so as to arrange the tension cord as an endless cord, wherein an overlapped joint portion of the tension cord is formed into an arcuate shape protruding on the outer circumferential side of the crawler.
A portion of the elastic crawler corresponding to the overlapped joint portion of the tension cord may be cured and molded in a mold so as to assume an arcuate shape protruding on the outer circumferential side of the crawler.
The radius of arc of the overlapped joint portion of the tension cord is preferably 1 to 2 times as large as the radius of a drive wheel round which the elastic crawler is wrapped.
Another technical means is a method of producing an elastic crawler including a crawler body made of a rubbery elastic material in a form of an endless belt, a tension cord being buried in the crawler body along the circumferential direction thereof, the tension cord having opposite ends which are joined together by overlapping one upon the other so as to arrange the tension cord as an endless cord. The method comprises steps of: molding a belt-like crawler body having opposite ends, overlapping the ends of the molded crawler body one upon the other, and curing and molding the overlapped portion to produce an endless elastic crawler. The overlapped portion of the molded crawler body is cured and molded in a mold so as to assume an arcuate shape protruding on the outer circumferential side of the crawler.
Another technical means of the present invention is a method of producing an elastic crawler including a crawler body made of a rubbery elastic material in a form of an endless belt, a tension cord being buried in the crawler body along the circumferential direction thereof, the tension cords having opposite ends which are joined together by overlapping one upon the other so as to arrange the tension cord as an endless cord. The method comprises steps of: molding a belt-like crawler body having opposite ends, overlapping the ends of the molded crawler body one upon the other, and curing and molding the overlapped portion to produce an endless elastic crawler. The overlapped portion is pre-molded in the overlapping process so as to assume an arcuate shape protruding on the outer circumferential side of the crawler.
A still another technical means of the present invention is a method of producing an elastic crawler including a crawler body made of a rubbery elastic material in a form of an endless belt, a tension cord being buried in the crawler body along the circumferential direction thereof, the tension cords having opposite ends which are joined together in an endless manner by overlapping one upon the other so as to arrange the tension cord as an endless cord. The method comprises steps of: molding a belt-like crawler body having opposite ends, overlapping the ends of the molded crawler body one upon the other, and curing and molding the overlapped portion to produce an endless elastic crawler. The overlapped portion is pre-molded in the overlapping process so as to assume an arcuate shape protruding on the outer circumferential side of the crawler and, then, the pre-molded overlapped portion is cured and molded in a mold so as to assume an arcuate shape protruding on the outer circumferential side of the crawler.
The radius of arc of the overlapped portion of the molded crawler body is preferably 1 to 2 times as large as a radius of a drive wheel around which the elastic crawler is wrapped.